The present invention relates to damping mechanisms, and is directed more particularly to single-use damping mechanisms which include an improved pressure actuated orifice seal and a compact internally disposed pressure relief assembly.
Damping mechanisms have long been known and used to limit, to safe maximum values, the rates or speeds at which moving objects can move between two positions. Such damping mechanisms are of two basic types. A first type, which is known as a multi-use or continuous-duty damping mechanism, is designed to be used again and again over an extended period of time. One example of such a damping mechanism is a door closer, which limits to a safe maximum value, the speed at which a door can swing from its open to its closed position, and thereby assure that the closing of the door does not cause injuries or generate unacceptably loud sounds.
A second type of damping mechanism, which will be referred to herein as a single-use or expendable damping mechanism, is designed to be used only once. One example of a single-use damping mechanism is a deployment damper, a damping mechanism which is used to limit, to a safe maximum value, the speed at which the fin or other jointed part of a countermeasure device or weapon may move from its undeployed to its deployed position after being released from a naval vessel or aircraft. Other examples of single-use damping mechanisms include safety devices which are used in emergencies to prevent dangerously sudden changes in pressure or position.
While existing single-use damping mechanisms can be used in a wide variety of ordinary applications, i.e., applications which do not involve exposure to extremes of temperature or which do not require that the damping mechanisms be located within extremely small spaces, there are important applications which involve just such extremes. The deployment dampers which are used in countermeasure devices that are carried by high performance aircraft, for example, must be extremely small to fit into the spaces within which they are carried, and must be able to operate reliably even after having been exposed to the large changes in temperature that occur during the operation of such aircraft. Some existing damping mechanism designs cannot be used in such applications because the accumulators which they use to compensate for rod volume make them too heavy or bulky to be located in the spaces available for them. Other existing damping mechanisms are small enough that they can be located in the spaces available for them, but cannot be used in such applications because they achieve this small size by eliminating an accumulator, and thereby run the risk that temperature related pressure changes will cause leaks that can result in deployment malfunctions.
In view of the foregoing, it will be seen that a need exists for a single-use damping mechanism which is both compact and light in weight, and which remains ready for immediate use even after being exposed to large changes in temperature.
In accordance with the present invention, there is provided an improved single-use damping mechanism which is both compact and light in weight, and which remains ready for immediate use even after being exposed to substantial changes in temperature.
Generally speaking, the damping mechanism of the invention includes a piston having a first or distal end which fits within a first or proximal end of a chamber defined by a piston receiving member or housing. This piston receiving member, together with the chamber formed therein, is commonly referred to as a cylinder, even though neither the piston receiving member nor the internal chamber necessarily have a cylindrical shape. The second or distal end of the piston receiving member defines first and second passages which are disposed in fluidic series between the internal chamber and the ambient air. When the piston is in its rest or unactuated position, the space between the distal end of the piston and the distal end of the piston receiving member is filled with a fluid which remains chemically stable in the presence of large changes in temperature, which does not allow the piston or piston receiving member to corrode, and which has the ability to lubricate the movement of the cylinder along the chamber. The volume of this fluid filling is preferably so related to the viscosity of the fluid, the cross-sectional areas of the first and second passages, and the time period during which the mechanism is to damp the movement of the device to be damped, that the chamber becomes empty at the time that the device to be damped reaches its fully deployed position.
In accordance with one important feature of the present invention, the first or inner passage has a cross-sectional area which is preferably relatively small in relation to the cross-sectional area of the internal chamber. As a result, the first passage serves to control and limit the rate at which fluid can be expelled from the internal chamber, and thereby determine, if all other design variables are constant, the duration of the above-mentioned time period. This time period will be referred to herein as the damping time or damping period. The second or outer passage preferably has a cross-sectional area which is relatively large in relation to the cross-sectional area of the first passage, although it too may be small in relation to the cross-sectional area of the internal chamber. As a result, the size of the second passage has no significant effect on the damping time of the damping mechanism. The second passage therefore provides ample space for a sealing or blocking member of the type contemplated by the present invention without affecting the damping time of the damping mechanism.
In accordance with a second important feature of the present invention, the sealing member is held within second passage by a retaining member which is adapted to hold the sealing member in sealing relationship to the first or fluid release passage when the force which the device to be damped applies to the piston has less than a predetermined magnitude, and to allow the sealing member to unseal or otherwise open the first passage when this force has a magnitude greater than or equal to that predetermined magnitude. By designing the damping mechanism so that this predetermined magnitude is exceeded only when the device to be damped is being deployed, the sealing and retaining members assure that the damping mechanism both retains its operating fluid before deployment, and releases it at the desired rate during deployment. The various embodiments of the present invention differ from one another primarily as a result of differences in the manner in which the sealing and retaining members seal and unseal the first passage. In some embodiments, the damping mechanism is designed so that the sealing member not only unseals the first passage, but is ejected from the second passage and, consequently, from the damping mechanism as a whole. In other embodiments, the damping mechanism is designed so that the sealing member remains in place, but tears or ruptures to release the fluid through the first and second passages.
In a first embodiment, the retaining member is a metal element which has a ring or sleeve-like shape, and which is adapted to be press fit into the second passage distally of the sealing member. In this embodiment, the tightness of the fit is selected so that the force acting on the sealing member during deployment pushes both sealing member and the retaining member out of the second passage, thereby allowing fluid to escape from the internal chamber at the desired rate. In a second embodiment, the retaining member is designed so that it is fixedly secured to the sides of the second passage, and the sealing member is designed to have elastomeric properties that allow it to be extruded through the hole through the retaining member. In a third embodiment, the retaining member is designed to be sufficiently weak that it ruptures or tears during deployment. It will be understood, however, that these embodiments are exemplary only, and that other releasing mechanisms may be used in practicing the present invention.
In accordance with a third important feature of the present invention, the damping mechanism is provided with an internally disposed pressure relief assembly for preventing temperature-related pressure changes from dislodging the sealing member before the device to be damped is deployed. This pressure relief structure preferably takes the form of a cavity which is located inside of the shaft of the piston, and which is disposed in fluidic communication with the internal chamber of the damping mechanism through an end cap that comprises a filter having numerous fine pores. In preferred embodiments, this cavity is filled with a chemically inert compressible material, such as a closed-pore foam. This pressure relief assembly protects the damping mechanism from temperature-related pressure changes by allowing fluid to flow slowly from the internal chamber to the cavity within the piston shaft, and back again, as necessary to prevent the pressure of the fluid within the internal chamber from becoming high enough to allow fluid to leak out of the damping mechanism. Because the pores of the end cap are fine, i.e., small in relation to the size of the first passage, however, fluid cannot flow from the internal chamber to the pressure relief cavity rapidly enough to affect the ability of the piston to move along the chamber in the intended manner when the damping mechanism is used. Thus, the pressure relief structure of the invention operates only when its operation is beneficial.
Other objects and advantages of the invention will be apparent from the following description and drawings.